Non-aqueous secondary batteries (hereinafter, also referred to simply as “secondary batteries”) such as lithium ion secondary batteries have characteristics such as compact size, light weight, high energy density, and the ability to be repeatedly charged and discharged, and are used in a wide variety of applications. Consequently, in recent years, studies have been made to improve battery members such as electrodes for the purpose of achieving even higher non-aqueous secondary battery performance.
An electrode for a secondary battery, such as a lithium ion secondary battery, normally includes a current collector and an electrode mixed material layer formed on the current collector. The electrode mixed material layer is formed, for example, by applying, onto the current collector, a slurry composition in which an electrode active material, a binder-containing binder composition, and so forth are dispersed in a dispersion medium, and drying the applied slurry composition.
In order to further improve the performance of secondary batteries, attempts have been made in recent years to further improve binder compositions used in electrode mixed material layer formation.
For example, PTL 1 discloses a technique for producing an aqueous electrode binder by adding N-methyl-benzisothiazolin-3-one as a preservative to a water-soluble polymer used as a binder having a methacrylic acid monomer unit as a main component in a solid content ratio of 100/10 (water-soluble polymer/N-methyl-benzisothiazolin-3-one). In the aqueous electrode binder of PTL 1 and an aqueous electrode composition produced using the aqueous electrode binder, the water-soluble polymer itself displays dispersing ability and viscosity modification functionality, and a produced secondary battery has improved capacity maintenance rate and the like.
On the other hand, a water-soluble polymer including a repeating unit derived from (meth)acrylamide, for example, has been proposed (PTL 2) as a water-soluble polymer for use in production of a secondary battery from a viewpoint of providing a binder composition for a power storage device that enables production of a power storage device having excellent electrode close adherence and charge/discharge characteristics. It has been confirmed with respect to the binder composition for a power storage device of PTL 2 that sedimentation does not occur even after one month of refrigerated storage.